What does that mean, you ask? Well, according to Last.fm, it gives you answers to these questions:

"How frequently do you change your listening habits? How mainstream is your taste?"

Read the copmplete explanation on their website. Would be cool if they offered it for every user as a flash applet that actually showed the atist's names. Kind of like the Digg visualization tool, but for your personal music profile. Right now it's not too intuitive, but still kinda pretty.